Beauveria bassiana :A fungus to effectively combat pests

Technical articles - Diseases

Arboriculture Arboriculture Market gardening Market gardening Field crops Field crops Biocontrol Entomopathogenic fungus Pests Biological control

B. bassiana infecting a pest

Used for over a century, Beauveria bassiana is an entomopathogenic fungus now recognized as an effective biocontrol tool. Naturally present in soils, it helps control many pests by reducing the use of chemical insecticides. Thanks to its original mode of action, it fits within integrated crop protection approaches, especially in Organic Farming.

Origin of the practice and principle

Beauveria bassiana is an entomopathogenic fungus naturally present in soils of many temperate regions. It has been used in biological control since the 19th century. Discovered in 1835 by Agostino Bassi as the agent of white muscardine disease in silkworms, it is now recognized for its effectiveness against many pests in arboriculture, notably in protecting apple trees in Organic Farming . It is classified as a low-risk active substance under Regulation (EU) No 540/2011, and approved for organic farming in several commercial specialties (Naturalis, BotaniGard). Its effectiveness relies on its ability to infect insects directly, causing their death and promoting secondary dissemination in the environment. This fungus is relatively selective: it mainly targets pest insects without significantly affecting beneficial insects or other non-target organisms, making it suitable for integrated crop management.

Description of the technique

B. bassiana acts by contact. Its conidia, in the presence of a susceptible host, adhere to the insect's surface and germinate, infecting it without the need for ingestion. It develops inside the organism, causing host death by dehydration. This mode of action makes all stages (egg, larva, adult) susceptible, and the infected insect can transmit the fungus to other individuals during its movements. This ability makes it an interesting ally against various pests, such as whiteflies on tomato crops. However, its selectivity is not absolute: some sensitive beneficials may also be affected, requiring precise targeting of applications to preserve beneficial insects.

Penetration is facilitated by targeted enzymatic production: chitinases, proteases, and lipases attack cuticle components. Once in the hemocoel, the fungus colonizes all tissues and releases toxins, including beauvericin, which accelerate lethality . This toxin targets insect cells by disrupting their membranes but can also exhibit some toxicity to mammalian cells at high doses. Its use in biocontrol remains regulated, with commercial formulations evaluated for safety regarding humans and the environment.

Infection causes insect death within 3 to 7 days, depending on strain virulence, applied dose, and environmental conditions. The pest's body then becomes a substrate for external fungal development, releasing new spores, creating a secondary infectious cycle in the crop.

Details on the technique

Beauveria bassiana has a very broad spectrum of action, with over 700 recorded target species, belonging to various orders: Homoptera (aphids), Thysanoptera (thrips), Hemiptera (whiteflies, family Aleyrodidae), Diptera (fruit flies), Mites, Coleoptera (weevils, flea beetles, family Curculionidae), and Lepidoptera .

The fungus's speed of action depends on several factors, notably the strain used, applied doses, and climatic conditions, explaining a delay of 3 to 7 days before death of infected insects. Due to the relatively slow action kinetics, it is recommended not to wait for population outbreaks: application should be anticipated at the first signs of infestation, especially for species where the larval stage is most vulnerable.

Treatment efficacy closely depends on abiotic conditions (temperature, humidity, UV radiation) and the formulation used.

Furthermore, comparative trials show that oil emulsions and microencapsulated formulations offer better protection of conidia against desiccation or UV, significantly improving mortality rates in target pests compared to conventional wettable powders.

Implementation and use

Application of B. bassiana is mainly by foliar spraying, with moderate pressure (2 to 3 bars) to preserve conidia efficacy. Soil treatments are also documented for some subterranean pests. Conidia being sensitive to desiccation and UV radiation, interventions should preferably be carried out under favorable microclimatic conditions: relative humidity ≥ 60%, temperatures between 18 and 30 °C, and low sunlight (morning or late afternoon time slots).

The persistence of the fungus in the environment is limited, so several successive applications are necessary (generally 3 to 6 per pest cycle) at 5 to 10-day intervals, consistent with the development cycles of targeted pests and observed parasitic pressure. Treatments should be renewed every 7 days, or every 3 to 5 days under high parasitic pressure.

The agent is generally compatible with other biological control methods, notably certain entomophagous beneficials such as Encarsia formosa (Hymenoptera, Aphelinidae), provided direct application is avoided. It is recommended to space treatments and beneficial releases to limit negative interactions.

For example, trials in olive growing have shown variable effectiveness of B. bassiana against the olive fruit fly depending on humidity conditions and application frequency.

Equipment and costs

Application of Beauveria bassiana does not require specific equipment: a standard sprayer equipped with fine jet nozzles is sufficient, provided homogeneous coverage of foliage is ensured to guarantee contact between conidia and target insects.

The cost of an application varies depending on the formulation (wettable powder, oil emulsion, microencapsulation) and supplier but generally remains comparable to conventional insecticides. In practice, it ranges between €50 and €150 per hectare per treatment within an integrated pest management strategy.

Commercial formulations are sensitive to heat (> 30 °C) and excessive humidity. Their optimal shelf life is between 6 and 12 months, provided they are stored in a temperate location (< 25 °C, RH < 50%). The most advanced formulations offer better protection of spores against UV and desiccation, but have a higher unit cost.

Spatial scale and implementation technique

Beauveria bassiana is applied to a wide range of crops: vegetables, fruit trees, vine, horticulture, in open field or under cover. This fungus integrates well into both organic systems and conventional itineraries aiming to reduce inputs. Multiple treatments (3 to 6 applications) are common, but a single application may suffice within an integrated pest management (IPM) program combining other methods (parasitism, nets, traps), especially in greenhouses where the stable microclimate favors efficacy and persistence.

Approved commercial specialties, such as Naturalis® (strain ATCC 74040) and BotaniGard® (strain GHA), cover a wide spectrum of crops and can be used alone or within combined programs.

Treatments must be carried out during the pest's sensitive phase and under climatic conditions favorable to fungal development. It is not recommended to intervene during high heat, strong wind, or prolonged drought. In greenhouse cultivation, efficacy is often increased due to the more stable and humid microclimate.

Agronomic, economic, and social criteria

The agronomic interest of this fungus lies in its ability to limit pest populations while reducing chemical insecticide use. This reduction helps preserve beneficials and functional biodiversity, while delaying resistance development in insects. The product leaves no residues on crops and has very low toxicity to non-target fauna—whether beneficial insects, soil organisms, or other species such as birds—provided the formulations used are verified.

On the economic side, the impact varies by system. In high-value crops, the use of B. bassiana helps secure yields and maintain sanitary quality. In conventional systems, it offers an effective alternative or relay to reduce dependence on synthetic molecules.

From a social perspective, reducing exposure to chemical products improves applicator health and meets societal expectations for sustainable agriculture. The technique enjoys good acceptability, notably due to regulatory standards governing untreated zones and the use of low-risk substances.

Advantages and disadvantages

Advantages

• Wide spectrum of action on insects
• Compatible with integrated pest management strategies
• No toxicity to plants and crops
• Approved active substance and usable in organic farming
• Reduced risk of resistance in pests

Disadvantages and limits

• Reduced efficacy under unfavorable climatic conditions (drought, UV)
• Slower action than a chemical contact insecticide
• Requires multiple applications and optimal humidity conditions
• Risks of interactions with certain beneficials or soil microorganisms

Regulations

Beauveria bassiana is listed in Regulation (EC) No 1107/2009 concerning the placing of plant protection products on the market, and approved as an active substance since 2009. It appears in the annex of Commission Implementing Regulation (EU) 540/2011 among so-called "low-risk" substances (low-risk active substances, as per Article 22), under EU code 1302. Its listing allows use in organic agriculture, but organic producers are advised to verify, for each commercial product, the mention "usable in OF", as not all formulations necessarily have this approval.

Products based on B. bassiana are recognized as safe for users, provided individual protective measures (gloves, goggles, mask) are respected. Rare cases of opportunistic infections have been reported in immunocompromised individuals with prolonged exposure, without calling into question safety in agricultural contexts.

Access to commercial formulations of B. bassiana

In France, currently approved formulations are mainly wettable powders (WP) or oil dispersions (OD), although some microencapsulations are under experimental evaluation.

Naturalis - Beauveria bassiana ATCC 74040 (oil OD)

• Product sheet: Biogard / CBC — oil OD formulation, no MRL, re-entry interval 3 days, organic farming compatible.
• Online sales (e.g. organic aggregators, cooperatives like Unéal): Naturalis 1 L, strain ATCC 74040.

BotaniGard 22 WP - Beauveria bassiana strain GHA (wettable powder)

• Official site (Certis Belchim France): 500 g powder, approved, re-entry interval 8 h, use in organic farming.
• Available via Amazon France (0.5 kg) and platforms like eBay and DoMyOwn.com (about 1 lb / 0.45 kg).

Where to order?

• Specialized distributors: Certis Belchim, De Sangosse or professional groups (Unéal, Agrigem) — via cooperatives or professional channels.
• General marketplaces: Amazon, eBay, DoMyOwn.com — beware of regulations and required certificates (Certiphyto, applicator licenses).